E-cigarette users are being warned that vaping could increase the risk of heart attacks and strokes.

Hundreds of thousands of people have turned to e-cigarettes to help them stop smoking - but a new study says they could be putting themselves at risk.

Scientists in Stockholm, Sweden, tested the effects of e-cigarettes which contain nicotine on 15 health volunteers who had not used them before.

In the 30 minutes after vaping, there was a significant increase in blood pressure, heart rate and arterial stiffness.

Cigarettes kill more people in Hull than almost anywhere else (Image: Sam Farr)

Those who used e-cigarettes which did not contain nicotine saw no ill-effects.

Dr Magnus Lundback, of the Danderyd University Hospital, Karolinska Institute, said: "The number of e-cigarette users has increased dramatically in the last few years. E-cigarettes are regarded by the general public as almost harmless.